In the medical and pharmaceutical industries, affinity biosensors for detecting and analyzing bio-molecular interactions, both for point-of-care applications and high throughput screening, have seen rapid development in recent years. Surface plasmon resonance (SPR) is widely used in these bio-sensing applications due to several attractive features such as:                SPR is label-free and, therefore, requires no fluorescent tagging;        SPR operates in real-time to measure reaction kinetics;        SPR can be implemented in parallel to perform high throughput screening and detect multiple target elements; and        SPR provides quantitative affinity measurements.        
Several SPR biosensing systems are commercially available and have large established user bases. However, SPR biosensing systems are still the object of considerable efforts of research and development in both universities and the private sector. One of the reasons for this is that the medical and pharmaceutical researchers and industries require performance still higher than that the current SPR biosensing systems can deliver. Two challenges of SPR biosensing systems are the following:                To overcome sensitivity limitations due to non-specific adsorption; and        Efficient mixing at the microfluidic level for homogeneous and timely analysis.        